The present invention relates to a spring-loaded pressure relief valve, particularly for containers of pressurized fluids.
As is known, spring-loaded pressure relief valves are usually fitted on containers intended to contain pressurized fluids; such valves are designed to prevent the pressure from increasing beyond the limits for which the container has been manufactured.
The operating principle of these valves is based on the possibility to automatically discharge, without further intervention except for the intervention produced by the pressure of the involved fluid, a certified amount of fluid, so as to prevent the preset safety pressure from being exceeded, furthermore, interrupting such discharge when normal operating pressure conditions are reestablished.
Currently known spring-loaded pressure relief valves generally have a system for adjusting the opening pressure of the valve that is based on the compression of a spring, which by acting on the flow control piston that closes the discharge port of the valve contrasts the internal pressure that tends to open the piston.
The dimensions and shape of the port of the valve are defined so as to minimize the force applied to the spring in order to contrast the pressure inside the container.
The direct action of the spring on the piston, however, causes intense stress on the gasket of the sealing device, which, by being generally made of plastics acquires over time a deformation that corresponds to the shape of the valve port, consequently altering the initial set value.
In some cases, the difference between the initial set pressure and the actual intervention pressure, after a period of time that is not easy to quantify, exceeds the intended safety value and the device must be replaced.
Clearly, this situation forces to proceed to periodic inspections, with considerable financial burdens that can be further increased by the need to perform frequent valve replacements.
In order to try to solve this problem, solutions have already been devised, such as for example the one disclosed in patent FR2671156, which describes a spring-loaded pressure relief valve that, in order to reduce the force to be applied to the spring for contrasting the pressure inside the container, uses an auxiliary valve that controls a discharge port provided at a chamber that is formed in practice by the main piston, which has a passage that transfers into the chamber the pressure inside the container.
When an overpressure occurs, the auxiliary valve opens, and accordingly, since the pressure that acts on the main piston decreases, such piston opens, clearing a large port that allows the outward flow of the fluid that was causing the overpressure in the container.
This type of valve suffers several drawbacks, the first of which is constituted by the fact that the pressurized fluid is discharged in a radial direction with respect to the valve body, accordingly causing considerable problems in applications on tanks that contain flammable gases or liquids.
Furthermore, another problem is constituted by the fact that when it is necessary to replace the auxiliary valve, the intervention performed inevitably removes the setting of said valve and therefore in most cases it is necessary to disassemble the valve completely and to replace and consequently set the auxiliary valve directly at the factory, with the obvious associated problems.